Our goal is to employ structure based modeling using software and facilities available through the Computer Graphics Laboratory, and molecular biology to increase trypsin and serine collagenase specificity for substrates with His residues at the P1 position. A variant of trypsin capable of using a substrated assisted catalytic mechanism (Tn H57A) will be refined to increase its hydrolysis activity. In addition, a His57->Ala variant of serine collagenase will also be expressed and tested against similar substrates and further refined. Our eventual goal is to design a protease capable of selectively cleaving off His6 tags used for nickel column purification.